Formation testing method



Feb. 21, 1967 E. F. BRIEGER FORMATION TESTING METHOD Filed May 1964 5/77/776 1 E fi/v-eger INVENTOR.

ATTOF/Vfy ing into the well bore.

United States Patent M 3,305,014 FORMATION TESTING METHOD Emmet F. Brieger, Needville, Tex., assignor, by mesne assignments, to Schlumberger Technology Corporation, Houston, Tom, a corporation of Texas Filed May 6, 1964, Ser. No. 365,328 4 Claims. (Cl. 166-3) This invention relates to methods for obtaining fluid samples from earth formations traversed by a well bore and, more particularly, for a method of using wire line formation testers and reliably obtaining a fluid sample from unconsolidated earth formations.

Wire line formation testers are disclosed, for example, in Chambers Patent No. 2,674,313 and Desbrandes and Fields Patent No. 3,011,554 wherein the wire line apparatus is lowered into a well bore containing well fluids. At the level at which a formation test is desired, the tool is actuated to press an elastomer sealing pad against the side wall of the bore in sealing engagement therewith. The central portion of the sealing pad contains a rigid insert which is usually attached to a gun block, the insert having a forward opening normally closed by a frangible cap. A perforating device such as a shaped charge or bullet in the gun block is adapted, when detonated, to open the forward opening and produce a perforation in the earth formations. Thereafter, fluids from the earth formations flow through the perforation into the gun block and through a flow line conduit to a sample-receiving chamber. The sample-receiving chamber typically includes a piston supported above a water cushion and a low-pressure chamber. The pressure of the formation fluids acting on the piston displaces the water cushion through a restricted orifice into the low-pressure chamher. The water cushion and piston control the flow of fluids from the earth formations at a rate which permits a reliable fluid sample to be obtained. After a period of time has elapsed or the sample chamber is full, the sample chamber is closed by a seal valve, the sealing pad retracted from the borehole wall and the apparatus retrieved.

In unconsolidated sands, that is, sands which have a tendency to flow easily, it is desirable to use a flow snorkel rather than a perforating device, the snorkel tending to enter into the sands and minimize sand erosion while a sample is being withdrawn. Apparatus of this type is disclosed in Patent No. 2,965,176 to Brieger and Fields. As disclosed in the Brieger et al. patent, there is no front frangible cap and typically, as illustrated in one form of the patent, the snorkel has a driver piston which is pressure balanced by mud pressures on either side while go- The flow line through the snorkel to the sample-receiving chamber is closed by a break valve. When the test is desired, the sealing pad is placed into engagement with the wall of the borehole and the break valve opened. When the break valve is opened, fluids from earth formations fiow into the sampling chamher.

It has been appreciated that in either of the above apparatus there is a portion of the flow line at atmospheric pressure. This has caused a pressure-differential shock to the earth formations which caused seal failures many times because of very rapid erosion of sand.

It is accordingly an object of the present invention to provide new and improved methods for obtaining fluid samples from unconsolidated earth formations traversed by a well bore and eliminating shock to earth formations and the sealing member when testing.

The present invention involves a method of obtaining a fluid sample from earth formations traversed by a Well bore containing a control fluid by use of an instrument 3,3fl5,fl14

Patented Feb. 21, 1967 having a sampling system including a ported sealing pad member opening to a fluid communication passage which opens to a sampling chamber. The sampling chamber contains a floating piston separating the fluid communication passage from a fluid cushion and an orifice=connection separating the fluid cushion from a low-pressure chamber where the fluid cushion retards movement of the piston in the chamber when formation fluids enter the port in the sealing pad and pass through the passage to the piston. A normally closed valve is arranged in the sampling system to prevent transfer of the fluid cushion to the low-pressure chamber and the method of the present invention includes the step of, prior to flowing fluids from earth formations in the sampling system with the sealing pad in contact with the borehole wall, filling the fluid communication passage between the piston and the sealing pad with control fluid in the well bore at the pressure of the controlled fluids at the desired test level and releasing the fluid cushion of the sampling system by opening the valve.

FIG. 1 illustrates a view of part of an apparatus used in performing the method of the present invention;

FIG. 2 illustrates in diagrammatic form one type of apparatus for performing the method of the present invention; and

FIG. 3 illustrates in diagrammatic form another type of apparatus for practicing the method of the present invention.

It will be appreciated that the aforesaid patents referred to, and others, illustrate apparatus in detail so the present disclosure will be brief as to specific apparatus details not significant to the present invention.

Referring now to FIG. 1, there is shown a resilient rubber seal pad 10a on a backing member or support shoe 12a, and an oppositely disposed, back-up shoe 28. The sealing pad Ilia and back-up shoe 28 are arranged to be moved relative to support means and one another by hydraulic pressure acting on pistons 29. Springs 30 can be used for retraction purposes of the shoe and pad 20 extends between the snorkel 14 and the sample-receiving chamber 31 and includes a break valve. Also in the flow line 20 is a pressure gauge 32 for providing pressure indications to the surface via a conductor lead 33 of an armored cable 32 in a well-known manner.

The sample-receiving chamber 31 includes a piston 33 supported above a water cushion 34, the water cushion being separated from a low-pressure chamber 35 by a restricted orifice 36. The opening to the sample-receiving chamber 31 is adapted to be closed by a seal valve 37 which includes a closure member 38 to close off the opening to the sample chamber and be locked in a closed position in a well-known manner. The seal valve 37 is actuated by hydraulic pressure and, in fact, the same hydraulic pressure to pistons 29 which is used to activate the pack-off shoe and back-off shoe can be used to activate the seal valve.

Hydraulic pressure for actuating seal valve 37 can be derived from the pressure line 40 which conducts fluid pressure from a hydraulic system 41 to the pistons 29 of the pack-off shoes. Line 40 can include an additional pressure line 42 to the seal valve 37 and a normally closed break valve 43. Thus, when the break valve 43 is operated, hydraulic pressure in pressure line 40 is applied via line 42 to the seal valve 37 to close the sample-- receiving chamber 31. Also, between the break valve 43 and seal valve 37 a dump chamber 44 can be provided for receiving the fluid under pressure from the hydraulic system 41 so as to reduce the hydraulic pressure on pistons 29 to a sufiiciently low value which permits the pads to retract from the wall of the borehole.

Snorkel 14 can be selectively operated by hydraulic pressure by coupling of an area 15 behind snorkel 14 to flow line 42 via a line 42a and break valve 4212. Thus, at the time valve 42b is opened, the snorkel 14 is operated.

The hydraulic actuating system 41 may be any of the well-known types which use pistons or the like operated by mud pressure applied to produce a sufiicient operating pressure in the flow line 40 for operation of the pad. The hydraulic system 41 is normally inoperative because of a break valve 45, the break valve 35, when open. coupling mud in the well bore to the piston of the hydraulic system for its operation. Also in the pressure line 49 of the hydraulic system is a pressure-recording means 4,6 for determining the pressure in the hydraulic system.

The apparatus of FIG. 1 may be used in performing the method of the present invention in the following manner: The apparatus is lowered into the well bore to a level where the test is desired. At this point, it will be appreciated that the snorkel 14 is in the position shown and mud at hydrostatic pressure fills the snorkel 14 through port 17 to break valve 19. Between break valve 19 and sample-receiving chamber 31, a portion of the flow line 20 is at atmospheric pressure. The present method contemplates the step of entirely filling the fluid communication passage between the piston 33 and the sealin g pad 10a with mud at hydrostatic pressure prior to flowing fluids from the earth formations with the sealing pad in sealing contact with the borehole wall. To do this with the apparatus of FIG. 1, before the pads are brought into contact with the Wall of the well bore, valve 19 is operated. Since valve 19 is a break valve operated by an igniter (not shown), electrical cur-rent from a surface control 48 supplied via a cable conductor 1'9 will operate the valve. Control 48 includes a source of power 49 and switch 51) to selectively apply power to the cable conductors. Valve 19, when opened, permits mud from the well bore to enter into the flow line 20 to the samplereceiving chamber 31. Immediately after operation of valve 19, the break valve 45 is operated to actuate the hydraulic system 41 and place the sealing pad 10a in sealing contact with the wall of the Well bore. This is accomplished by connecting switch 50 to conductor 45. It has been determined that the quantity of mud received by the sample-receiving chamber 31 while the valve 19 is open is relatively negligible insofar as the test results are concerned and the very beneficial result obtained by this operation minimizes and eliminates seal failures in unconsolidated sands. This is because the fluids are at hydrostatic pressure from the snorkel 14 to the piston 33 in the sample-receiving chamber 31 before the seal is made and this considerably reduces the pressure differential existing between the fluids in the earth formations and the sample-receiving chamber. Thus, severe differential pressures are not applied across the earth formations and erosion of earth formations due to such a pressure differential is minimized.

After obtaining a seal, valve 421) is opened by connecting switch 5% to conductor 42' and snorkel 14 can assist in sampling and maintaining the pad seal on the borehole wall.

After the sampling period, the seal valve 37 is operated by actuating break valve 43 (switch 54) to conductor 43') and a get-away shot (not shown) in the block 11a is operated to balance pressure across the seal p ad. Dumping of the hydraulic fluid in chamber 44 permits retraction of the sealing pad from the well bore wall.

The pressures are recorded by recorder R, the signals from device 32, 46 being transmitted via conductor wires 33, 46'.

Referring now to FIG. 2, as in FIG. 1, a sealing pad 16 of rubber or the like is shown attached to a rectangular'ly shaped sampling lock member 11. The sealing pad 18 is adapted to be pressed into engagement with the side wall of a borehole by end connections 12. Although it will be appreciated by those skilled in the art that there are a variety of ways for placing the pad in tight, sealing engagement with the wall of a borehole, it is pre ferred to use apparatus of the type disclosed in the aforesaid patents.

The sampling block member 11 of FIG. 1 includes a central bore 13 with first and second portions 13a, 136 respectively having a different diameter. Bore 13 of block member 11 as shown would normally slidably and sealingly receive a sampling snorkel tube and accompanying piston. As shown in the drawing, the portion 13a of the bore 13 is opened to the well fiuid to one sideof the body member at 16 so that mud pressure in the well bore could act upon a piston tending to urge it and an attached sampling tube toward and into the earth formations when a pressure diiferential exists across the piston. However, for purposes of the present invention, the snorkel tube and piston are removed and a solid piston slidably and sealingly received in bore portion 13a. Bore portion 13:: is ported at 17 to a chamber 18 which, in turn, couples to a break valve 19. The break valve 19 typically includes a breakable, hollow, closed end member which normally closes a passageway 20 to a sampling chamber. A hammer 21 is mounted in block member 11 so as to be moved by the force of an explosive ignited by an igniter 22 and break open the closed opening 20 to the sampling chamber.

Also shown in the block member 11 is a pressureequalizing device 23 known as a get-away shot which includes a small piston 24, an electrical igniter 25, and an intermediate chamber 26 filled with an explosive. When the igniter detonates the explosive in chamber 26, the entire passageway from front to back of the body member 11 is opened thus placing mud pressure in the well bore in fluid communication with the sealed-off interior of the block member so that the pressure across pad 10 is equalized thereby facilitating retraction of the pad. Further discussion of this type of apparatus is not necessary since reference to the prior art will amply illustrate the type of apparatus which can be used in the present method.

The apparatus of FIG. 2 is substantially the same as the apparatus of FIG. 1 except for the removal of the snorkel 14 and associated valve 42b. As will be appreciated, there is no penetrating means associated with the block 11 of FIG. 2.. The equalization of pressures in flow line 26 is accomplished as before, i.c., the valve 19 is opened and the seal pad 10 immediately thereafter set against the wall of the borehole.

Referring now to FIG. 3, in this type of apparatus an opening 13c in a block 11 is coupled directly to the sample-receiving chamber 52 by a flow passage 53. Thus, during the entire trip into the well with the tool, the mud in the well bore first fills the passage 53 to the sample-receiving means 52 and the pressure on the piston 54 is dependent on the hydrostatic pressure of the mud in the well bore. In the sample-receiving means 52, a valve 54a is provided between the water cushion 56 and the atmospheric chamber 57 of the sampling means which prevents the water cushion 56 from being displaced in the chamber 57 while the tool is lowered into the well bore.

This apparatus can be used to perform the method of the present invention in the following manner: The valve is opened to actuate the hydraulic system and place the pad 16a in sealing contact with the well bore wall. It will be rememberd that the entire flow line 53 to the piston of the sample-receiving means 52 is filled with mud at the hydrostatic pressure in the well bore. Next, the valve 54a in the sample chamber is opened thereby releasing the water cushion 56 and fluids from the earth formations may now flow into the sample-receiving means 52. After a sufiicient period of time for the test has elapsed, the sealing valve 37 and get-away are operated, and as before, the pads retract and the tool may be brought to the surface.

One important aspect of the present invention which is accomplished by the present invention and should not be overlooked is the fact that by subjecting the piston in the sample-receiving chamber to the mud pressure in the well bore before admitting well fluids from earth formations, the water cushion may be compressed to whatever extent the hydrostatic pressure calls for. While this on its face may not appear significant, it has been realized by the inventor that in the well bore under the pressures encountered, oftentimes water, a seemingly incompressible fluid, in fact is compressible. This compressibility of water in a well tool creates a volume or space at lower pressure in the well tool. This also contributes to the pressure differential between the earth formations and the well tool. In the case of unconsolidated formations, this causes flowing and erosion of the sand and the sealing pad fails to effectively hold a seal. Therefore, the present invention solves an extremely significant problem of failure of the pad to seal against the well bore wall when the formations are unconsolidated and obtains reliable tests where heretofore none were possible.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for obtaining fluid samples from earth formations traversed by a well bore containing mud comprising the steps of: admitting a limited quantity of mud to a fluid sample-receiving chamber to normalize the pressure in the sample-receiving chamber to the hydrostatic pressure of the mud, sealing off a selected zone of earth formations While said quantity of mud is in said chamber, and establishing a flow of fluids from earth formations to said sample-receiving chamber.

2. A method for obtaining fluid samples from earth formations traversed by a well bore containing mud comprising the steps of: admitting a limited quantity of mud to a fluid sample-receiving chamber to normalize the pressure in the sample-receiving chamber to the hydrostatic pressure of the mud, sealing off a selected zone of earth formations while said quantity of mud is in said chamber, establishing a flow of fluids from earth formations to said sample reoeiving chamber, and enclosing a sample of fluids in said chamber.

3. A method for obtaining fluid "samples from earth formations traversed by a well bore containing mud comprising the steps of: suspending in a well bore a samplereceiving tool, admitting a limited quantity of mud to a fluid sample-receiving portion of said tool to normalize the pressure in said sample-receiving portion to the hydrostatic pressure of the mud, sealing off a selected zone of earth formations while said quantity of mud is in said portion, establishing a flow of fluids from earth formations to said sample-receiving portion, and enclosing a sample of fluids in said portion.

4. In a method of obtaining fluid samples from earth formations traversed by a well bore containing a control fluid and using an instrument having a sampling system including a ported sealing pad member opening to a fluid communication passage which opens to a sampling chamber which contains a floating piston separating the fluid communication passage from a fluid cushion, and an orifice connection separating the fluid cushion from a low-pressure chamber where the fluid cushion retards movement of the piston in the chamber when formation fluids enter the port in the sealing pad and pass through the passage to the piston, and a normally closed valve arranged in said sampling system to prevent transfer of the fluid cushion to said low-pressure chamber, the method including, prior to flowing fluids from earth formations in the sampling system with the sealing pad in contact with the borehole wall, the step of filling the fluid communication passage between the piston and sealing pad with control fluid in the well bore at the pressure of the control fluids at the desired test level and releasing the fluid cushion of the sampling system by opening the valve.

References Cited by the Examiner UNITED STATES PATENTS 2,612,346 9/1952 Nelson 166-100 X 2,640,542 6/1953 Brown et a1. 166-100 X 2,905,247 9/1959 Vestermark 166-100 3,079,793 3/1963 Le Bus et al 166-100 X 3,104,712 9/1963 Whitten 166-100 3,173,485 3/1965 Bretzke 166-100 CHARLES E. OCONNELL, Primary Examiner. D. H. BROWN, Assistant Examiner. 

1. A METHOD FOR OBTAINING FLUID SAMPLES FROM EARTH FORMATIONS TRAVERSED BY A WELL BORE CONTAINING MUD COMPRISING THE STEPS OF: ADMITTING A LIMITED QUANTITY OF MUD TO A FLUID SAMPLE-RECEIVING CHAMBER TO NORMALIZE THE PRESSURE IN THE SAMPLE-RECEIVING CHAMBER TO THE HYDROSTATIC PRESSURE OF THE MUD, SEALING OFF A SELECTED ZONE OF EARTH FORMATIONS WHILE SAID QUANTITY OF MUD IS IN SAID CHAMBER, AND ESTABLISHING A FLOW OF FLUIDS FROM EARTH FORMATIONS TO SAID SAMPLE-RECEIVING CHAMBER. 